This invention relates to parachute systems and methods of controlling parachute deployment.
Drogue parachutes are commonly deployed for stabilization or airspeed retardation. Often, the drogue parachute is deployed to decelerate an object to an airspeed at which a larger parachute can be safely inflated. Drogue parachutes are commonly used in aerial cargo and personnel delivery systems, spacecraft landing systems, and on aircraft and aircraft ejection seats.
It is often necessary while towing a drogue parachute to provide a trigger signal that initiates further events once certain parameters are met. Drogue parachutes typically are not themselves directly used to trigger any subsequent events. Rather, subsequent events are triggered by independent sensing of predetermined parameters. For example, an air pressure threshold corresponding to a target altitude triggers release of the drogue parachute and deployment of the main parachute as shown in U.S. Pat. No. 5,899,415. Alternative systems trigger release after a predetermined time since drogue deployment, or once measured airspeed drops below a predetermined value. Examples are shown in U.S. Pat. Nos. 5,474,257, 5,884,863 and 7,059,570.
Other systems employ more sophisticated triggering schemes incorporating combinations of altitude, time, and/or airspeed data. One common scheme triggers drogue parachute release and main parachute deployment only when both altitude and airspeed have dropped below predetermined values, as shown in U.S. Pat. No. 4,505,444. Another scheme releases the drogue parachute once the drogue parachute has both remained deployed for a predetermined time interval and dropped below a predetermined altitude threshold. U.S. Pat. Nos. 5,064,151 and 6,889,942 use this system.
Parachute systems capable of incorporating multiple parameters into the event triggering scheme enable superior system reliability and performance. Prior art systems in which event triggering is a function of airspeed, however, require independent means for directly sensing airspeed. The autonomy and utility of such systems is therefore limited.